Method of manufacturing a capacitor in a semiconductor device

ABSTRACT

The present invention relates to a method of manufacturing a capacitor in a semiconductor device. It is designed to solve the problem due to oxidization of the surface of the underlying tungsten electrode during thermal process performed after depositing Ta 2 O 5  to form a dielectric film in a Ta 2 O 5  capacitor of a MIM (Metal Insulator Metal) structure using tungsten (W) as an underlying electrode. Thus, the present invention includes forming a good thin WO 3  film by processing the surface of the underlying tungsten electrode by low oxidization process before forming a Ta 2 O 5  dielectric film and then performing deposition and thermal process of Ta 2 O 5  to form a Ta 2 O 5  dielectric film. As a good WO 3  film is formed on the surface of the underlying tungsten electrode before forming a Ta 2 O 5  dielectric film, the grain boundary of the tungsten film is filled with oxygen atoms, thus preventing diffusion of oxygen atoms from the Ta 2 O 5  dielectric film during a subsequent thermal process. Also, as a further oxidization of the surface of the underlying tungsten electrode by the WO 3  film could be prevented, thereby improving the characteristic of the leak current of the Ta 2 O 5  capacitor.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates generally to a method of manufacturing a capacitorin a semiconductor device, and more particularly to, a method ofmanufacturing a capacitor in a semiconductor device which can preventoxidization of the surface of an underlying electrode to improve thecharacteristic of the leak current of a Ta₂O₅ capacitor, upon a thermaltreatment process performed after Ta₂O₅ is deposited in order to form adielectric film, in a Ta₂O₅ capacitor of a MIM (Metal Insulator Metal)structure using tungsten (W) as an underlying electrode.

2. Description of the Prior Art

Generally, when manufacturing a Ta₂O₅ capacitor in a memory device, ifmetal materials such as Tungsten are used as underlying electrodematerials, the work function of the metal materials with poly-silicon islarge. Thus, the thickness of the effective oxide film Tox can bereduced and thus the leak current in the thickness of the same effectiveoxide film can also be reduced. Further, the value of Δ C depending onthe bias voltage is small. As a Ta₂O₅ dielectric film lacks oxygen inthe film formed by Ta₂O₅ deposition process and also contains impuritiessuch as carbon or hydrogen etc., in order to secure the dielectriccharacteristic of the Ta₂O₅ capacitor, oxygen must be flowed into it anda subsequent process for removing impurities must be performed after theTa₂O₅ deposition is completed.

This subsequent process is mainly thermally performed under oxygenatmosphere at a higher temperature, thus securing the dielectriccharacteristic of a Ta₂O₅ dielectric film. However, if the temperatureof the thermal process is too high or the time of the thermal treatmentis too long, upon thermal treatment process, the surface of theunderlying tungsten electrode is oxidized to form a WO₃ film. The WO₃film has the dielectric constant of about 42, which is higher than thatof Ta₂O₅ dielectric film having about 25. However, when creating the WO₃film, there is a possibility that oxygen within the Ta₂O₅ dielectricfilm can be diffused into the underlying tungsten electrode. Also, dueto the difference of the thermal expansion coefficient with the Ta₂O₅dielectric film, there is a problem that the characteristic of the leakcurrent of the Ta₂O₅ capacitor becomes degraded since a phenomenon offilm lifting of the film is generated.

SUMMARY OF THE INVENTION

It is therefore an object of the present invention to provide a methodof manufacturing a capacitor in a semiconductor device which can preventoxidization of the surface of an underlying electrode to improve thecharacteristic of the leak current of a Ta₂O₅ capacitor, upon a thermaltreatment process performed after Ta₂O₅ is deposited in order to form adielectric film, in a Ta₂O₅ capacitor of a MIM (Metal Insulator Metal)structure using tungsten (W) as an underlying electrode.

In order to accomplish the object, a method of manufacturing a capacitorin a semiconductor device according to the present invention ischaracterized in that it comprises the steps of forming an underlyingtungsten electrode on a substrate in which an underlying structure isformed; forming a WO₃ film on the surface of the underlying tungstenelectrode; forming a Ta₂O₅ dielectric film on the WO₃ film; and formingan upper electrode on the Ta₂O₅ dielectric film.

BRIEF DESCRIPTION OF THE DRAWINGS

The aforementioned aspects and other features of the present inventionwill be explained in following description, taken in conjunction withthe accompanying drawings, wherein:

FIGS. 1A through 1D are sectional views for illustrating a method ofmanufacturing a capacitor in a semiconductor device according to thepresent invention; and

FIG. 2 is a graph of I-V characteristic for showing the leak currentcharacteristic of a capacitor depending on a thermal process under a lowtemperature oxygen atmosphere before a Ta₂O₅ dielectric film is formed.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

The present invention will be described in detail by way of a preferredembodiment with reference to accompanying drawings, in which likereference numerals are used to identify the same or similar parts.

FIGS. 1A through 1D are sectional views for illustrating a method ofmanufacturing a capacitor in a semiconductor device according to thepresent invention.

Referring now to FIG. 1A, a first doped poly-silicon layer 1 is formedon a substrate 10 in which an underlying structure is formed. Then, abarrier metal layer 2 is formed on the first doped poly-silicon layer 1.

In the above, the barrier metal layer 2 is formed of a Ti film and a TiNfilm. The Ti film is formed by depositing Ti in 100 through 200 Åthickness by means of sputtering method. The TiN film is formed in 100through 200 Å thickness by means of metal organic chemical vapordeposition (MOCVD) method using Ti(N(CH₃)₂)₄(TDMAT) as raw materials andusing He and Ar as carrier gases. At this time, the depositionconditions include 200-300 sccm in the flow rate of raw materials; 100through 300 sccm in the flow rate of He and Ar, respectively, beingcarrier gases; 2-10 Torr in the pressure within the reactive furnace and300-500° C. in the temperature within the reactive furnace. Thereafter,a plasma process is performed for about 20 through 50 seconds with thepower of 500 through 1000W.

Referring now to FIG. 1B, a tungsten film 3 is formed on the barriermetal layer 2 to complete an underlying electrode.

In the above, the tungsten film 3 is formed by chemical vapor deposition(CVD) method under the conditions that WF₆ is used as raw materials, H₂is used as a reactive gas, the pressure within the reactive furnace ismaintained at 80-110 Torr, and the temperature within the reactivefurnace is maintained at the temperature of 350-450° C.

Referring to FIG. 1C, after removing a native oxide film in whichimpurities created on the surface of the tungsten film 3 are containedby means of cleaning process, a WO₃ film 100 is forcedly formed on thesurface of the tungsten film 3. Then, a Ta₂O₅ dielectric film 4 isformed on the WO₃ film 100.

In the above, the cleaning process is performed using 50:1 HF for 30through 50 seconds. The WO₃ film 100 is formed in thickness of 10-30 Åby oxidizing the tungsten film 3 by means of Rapid Thermal Anneal (RTA),plasma process or UV/O₃ process etc. under a low temperature oxygenatmosphere. The WO₃ film 100 formed thus is good in the quality of thefilm and also fills the grain boundary of the tungsten film 3 withoxygen atoms. The rapid thermal process is performed under theatmospheres of O₂ or N₂O at the temperature of 450-550° C. for 5-20seconds. The plasma process is performed under the atmospheres of O₂ orN₂O at the temperature of 300-550° C. for 30-120 seconds by the power of200-500W. The UV/O₃ process is performed at the temperature of 300 14550° C. for 2-5 minutes at the strength of 15-30 mW/cm².

The Ta₂O₅ dielectric film 4 is deposited with use Ta₂O₅ under theconditions that Ta(C₂H₅O)₅ is used as raw materials, N₂ gas and O₂ gasis used as a carrier gas and an oxidizer, respectively, the flow rate ofthe N₂ gas is maintained at 350-450 sccm, the flow rate of the O₂ gas ismaintained at 20-50 sccm, the pressure within the reactive furnace ismaintained at 0.1-0.6 Torr, and the temperature within the reactivefurnace is maintained at 350-450° C. Then, in order to preventoxidization of the tungsten film 3 being an underlying electrode whileobtaining a dielectric characteristic, the Ta₂O₅ dielectric film 4 isexperienced by a rapid thermal process by mixing inactive gases such asN₂, Ar, He etc. in N₂O gas or O₂ gas at the temperature of 550-700° C.for 20-60 seconds, or by a plasma annealing process under oxygenatmosphere using O₂ gas or N₂O gas by which a plasma power of 10-100W isapplied at the temperature of less 350° C.

Referring to FIG. 1D, a TiN film 5 and a second doped poly-silicon layer6 are sequentially formed on the Ta₂O₅ dielectric film 4, thuscompleting an upper electrode of a capacitor. By means of a series ofthese processes, a Ta₂O₅ capacitor of a MIM structure is manufactured.

In the above, the TiN film 5 is formed in thickness of 200-500 Å bymeans of chemical vapor deposition (CVD) method under the conditionsthat TiCl₄ is used as raw materials, NH₃ gas is used as a reactive gas,the temperature within the reactive furnace is maintained at 300-500° C.and the pressure within the reactive furnace is maintained at 0.1-2Torr. The second poly-silicon layer 6 is formed in thickness of 800-1200Å. The TiN film 5 functions to reduce the work function with the secondpoly-silicon layer 6 and the Ta₂O₅ dielectric film 4.

FIG. 2 is a graph of I-V characteristic for illustrating the leakcurrent characteristic of a capacitor when comparing the methodaccording to the present invention by which O₂-RTA is performed at thetemperature of 500° C. under the atmosphere of oxygen with theconventional method in which no process is performed before a Ta₂O₅dielectric film is formed.

In order to compare the leak current characteristic, the Ta₂O₅dielectric films in the present invention and the conventional methodare formed identically. As shown in FIG. 2, the thickness of theeffective oxide film Tox is almost same in both cases of theconventional method and the present invention. However, it could be seenthat the leak current in the present invention has been greatlyimproved. In other words, , the leak current at 1V in the conventionalmethod shows 4.32E-5(A/cm²) while that in the present invention shows2.58E-8(A/cm²). Also, it could be seen that the leak current in thepresent invention is greatly improved even in the negative voltage.

As can be understood from the above description with the presentinvention, the present invention forms a good WO₃ film on the surface ofthe underlying tungsten electrode before forming a Ta₂O₅ dielectric filmin a Ta₂O₅ capacitor using tungsten as an underlying electrode. As thegrain boundary of the tungsten film is filled with oxygen atoms,diffusion of oxygen atoms from the Ta₂O₅ dielectric film can beprevented during a subsequent thermal process. Thus, the intrinsiccharacteristic of the Ta₂O₅ dielectric film can be intact. Also, afurther oxidization of the surface of the underlying tungsten electrodeby the WO₃ film could be prevented, thereby improving the characteristicof the leak current of the Ta₂O₅ capacitor.

The present invention has been described with reference to a particularembodiment in connection with a particular application. Those havingordinary skill in the art and access to the teachings of the presentinvention will recognize additional modifications and applicationswithin the scope thereof.

It is therefore intended by the appended claims to cover any and allsuch applications, modifications, and embodiments within the scope ofthe present invention.

What is claimed is:
 1. A method of manufacturing a capacitor in asemiconductor device comprising the steps of: forming an underlyingtungsten electrode on a substrate in which an underlying structure isformed; forming a WO₃ film on the surface of the underlying tungstenelectrode, wherein said WO₃ film is formed in thickness 10-30 Å byprocessing the surface of the underlying tungsten electrode by an UV/O₃process performed at a temperature of 300-550° C. for 2-5 minutes at astrength of 15-30 mW/cm²; forming a Ta₂O₅ dielectric film on the WO₃film; and forming an upper electrode on the Ta₂O₅ dielectric film. 2.The method of manufacturing a capacitor in a semiconductor deviceaccording to claim 1, further comprising the step of cleaning using 50:1HF for 30-50 seconds in order to remove a native oxide film in whichimpurities created on the surface of the underlying tungsten film arecontained, before the WO₃ film is formed.
 3. A method of manufacturing acapacitor in a semiconductor device comprising the steps of: forming anunderlying tungsten electrode on a substrate in which an underlyingstructure is formed; forming a WO₃ film on the surface of the underlyingtungsten electrode using an UV/O₃ process, wherein said UV/O₃ process isperformed at a temperature of 300-550° C. for 2-5 minutes at a strengthof 15-30 Mw/cm²; forming a dielectric film on the WO₃ film; and formingan upper electrode on the dielectric film.
 4. A method of manufacturinga capacitor in a semiconductor device according to claim 3, furthercomprising the step of removing a native oxide film from the tungstenelectrode prior to forming a WO₃ film.
 5. A method of manufacturing asemiconductor device according to claim 3, wherein said WO₃ film isformed in a thickness of 10-30 Å.
 6. A method of manufacturing asemiconductor device according to claim 3 wherein said dielectric filmcomprises Ta₂O₅.